A variant on this topic:
Notice when providing evidence X for a position P you believe in.
Bonus points for reviewing recent memories to see if you have supported P repeatedly, especially to the exclusion of evidence to the contrary.
Feel revulsion at having become the puppet of P.
Introduce a nudge away from P. Some examples:
Provide some good evidence counter to P.
If you cannot point to specific counter evidence, try to at least describe what counter evidence would look like.
State just how surprised you would be to see the evidence X if the position P were false. Can you rank it relative to other pieces of evidence under consideration? If the evidence is really weak, ask to have it weighted as such.
This seems sloppy, as it relies on the sense of revulsion to determine how much of a counter-nudge to give. It should still be useful, I hope.
The exercise to train this with:
Propose a character facing a choice, especially on topics that are muddled by being high-profile (e.g. Jane Senator must decide how to vote on extending unemployment benefits).
Provide a small selection of evidence that the character has considered, and state that their position after seeing just that evidence is for, against or undecided.
Ask the participants what additional evidence they think the character should consider.